1. Field of the Invention
The present invention relates to an ink jet recording apparatus for forming ink liquid droplets by discharging ink for the performance of recording. The invention also relates to an ink jet recording head used for such recording apparatus.
2. Related Background Art
It is generally practiced to provide a printer, a copying machine, a printing device for facsimile equipment or the like with the structure that prints images formed by dot patterns on a printing medium, such as paper, thin plastic sheet, or cloths, among some others, in accordance with image information. The printing apparatuses of the kind are classified into those using ink jet method, wire-dot method, thermal method, and laser beam method depending on the printing method adopted by each of them.
Of those ones, the ink jet method is such as to perform printing by discharging ink from a recording head to a printing medium. The ink jet method makes it possible to print images in high precision at high speed. Further, being of non-impact type, noises are smaller with such advantage that it is easier to print color images by use of multiple color ink.
Of the ink jet methods currently available, the bubble jet printing method invented by the applicant hereof makes it possible to discharge ink by the utilization of pressure exerted when liquid is heated to bubble. For the bubble jet printing method, heaters that heat liquid can be arranged in high density easily. Thus, as an advantage, among many, that this method provides, an apparatus can be structured with ease for the performance of high-resolution printing at high speed.
For the ink jet recording apparatus of bubble jet printing method, ink is usually used as printing liquid. Therefore, with the evaporation of ink, its viscosity may change or with possible mixture of bubbles in ink, the performance of ink discharge is affected by such causes to produce unfavorable effect on prints in some cases.
More specifically, at the early stage of the installation of an ink jet recording head on an ink jet recording apparatus or at the time of exchanging ink tanks, the mixture of bubbles occurs in ink when ink is filled in the ink jet recording head. Also, as time elapses, even in a state where ink is filled in the ink jet recording head, the air may be allowed to enter the discharge ports that discharge ink or fitting portions of ink supply passages. Then, in some cases, bubbles may be created in ink. If such bubbles exist in a large amount in the vicinity of ink discharge portion, discharges are disabled (causing non-discharge) to change the ink discharge amounts and discharge speeds, hence impeding the normal recording in some cases.
Here, therefore, it is necessary to adopt the technology and technique specially made available for reliably maintaining the ink discharge function of the recording head for an ink jet recording apparatus. Among such technologies and techniques, there is known a method in which suction recovery process is executed to suck ink, which resides in the vicinity of the discharge portion, from the recording head for appropriately removing mixed bubbles and overly viscous ink together with ink thus sucked out. The head recovery device that executes the suction recovery process is generally structured with a cap for capping, which closely covers the discharge port surface where discharge ports of the recording head are open, and a suction pump that performs suction inside the cap. The suction recovery process executed by the head recovery device is such that the recording head moves to the position facing the cap, and after capping, the inside of the cap is sucked by use of the suction pump, and then, bubbles and overly viscous ink in the recording head are sucked and removed together with ink sucked out at that time. The suction recovery process of the kind is now an important art among the technologies and techniques for reliably maintaining an ink jet recording apparatus.
In recent years, it has been required that the ink jet recording apparatus should record images in the so-called high quality having precisely adjusted gradation therefor. As one of the methods that make the formation of such images possible, it is devised to provide the discharge units for one recording head in order to discharge liquid droplets in different discharge amounts. In such a case, the balance required for desirable performance of discharges may differ on various aspects per discharge unit, which makes it impossible to execute any stabilized operation of recording sometimes.
For example, usually, for the discharge portion where liquid droplet is discharged in a comparatively large amount (hereinafter referred to as a large discharge portion), the discharge port area and the sectional area of the flow path communicated with the discharge port are made larger than the discharge portion where liquid droplet is discharged in a comparatively small amount (hereinafter referred to as a small discharge portion). As a result, the flow resistances in the large discharge portion and the small discharge portion are made different greatly. Therefore, the characteristics of bubble removal become different when these portions are covered by one cap, and the suction recovery process is made under the same condition.
Also, as compared with the large discharge portion, the small discharge portion is easier to be affected by the higher viscosity of ink resulting from evaporation, because the area of the discharge port is smaller to make the flow resistance higher. Consequently, when a recording operation is executed after a specific time elapses without any recording operation, there is a fear that non-discharge takes place in the small discharge portion at the time of the first shot of ink or there is encountered a phenomenon (called viscous plug phenomenon) that a desired amount of discharge cannot be obtained.
Also, the characteristics of refilling, that is, the refilling of liquid subsequent to the liquid discharge, are made different in the large discharge portion and the small discharge portion, thus resulting in a fear that stabilized liquid discharges cannot be performed.
Also, if a structure is arranged so that liquid is supplied from one liquid supply port to the large discharge portion and the small discharge portion, the vibration of liquid exerts influence on the small discharge portion nearby, which is propagated from the large discharge portion when liquid is discharged from that portion, and there is a fear that stabilized liquid discharges cannot be performed.
Now, therefore, with attention given to the technical problems discussed above with respect to the conventional art, the present invention is designed. It is an object of the invention to provide an ink jet recording head with intermixed large discharge portion and small discharge portion, which is capable of performing stabilized recording with various balances well kept for the large and small discharge portions, and also, to provide an ink jet recording apparatus having such ink jet recording head mounted thereon.
It is another object of the invention to provide an ink jet recording head with intermixed large discharge portion and small discharge portion, for which it is attempted to reduce the influence of liquid vibrations propagated when liquid is discharged from discharge ports nearby in the small discharge portion, while enhancing the refilling characteristics in the small discharge portion to make stabilized recording possible, and also, to provide an ink jet recording apparatus having such ink jet recording head mounted thereon.
In order to achieve the aforesaid objects, the ink jet recording head of the present invention comprises a first discharge portion for discharging liquid from a first discharge port as liquid droplet in a specific amount, a second discharge portion for discharging liquid from a second discharge port as liquid droplet in a larger amount than that of the first discharge portion, and an opening provided only for the first discharge portion, being open to the opening surface of the first discharge port and communicated with the first discharge port without discharging liquid droplet.
With the structure thus arranged, it is made possible to enable the flow resistance of the discharge port portion having the small discharge amount of liquid to be discharged to be close to the flow resistance of the discharge portion having the large discharge amount of liquid to be discharged when suction recovery process is executed. Therefore, even if the discharge ports of discharge portions, both of them, are covered by one cap for the execution of the suction recovery process, liquid can be sucked out equally from both of them, hence making it possible to perform the process appropriately for both of them. Also, for the discharge portion having the small discharge amount of liquid to be discharged, it is possible to execute the suction recovery process in good condition by enabling a comparatively small suction to act thereon. As a result, it becomes possible to reduce such drawback, as deformation or breakage of the discharge port plate, which may be caused by the suction recovery process.
Also, with the provision of the aforesaid opening, it is made possible to raise the environmental moisture in the vicinity of the discharge ports of the discharge portion having the small amount of liquid to be discharged. As a result, even if discharge is not made for a certain period of time, it becomes possible to suppress making the viscosity of ink higher in the vicinity of such discharge ports, thus reducing the occurrence of the viscous plug phenomenon. Furthermore, it is made possible to reduce the influence of liquid vibrations exerted in the small discharge portion, which is propagated at the time of discharging liquid from the discharge ports nearby, so as to obtain the action that may stabilize discharges, and also, it is possible to obtain the action that may accelerate the refilling speed in the small discharge portion by the function of capillary force on the opening portion when liquid is refilled again after liquid is discharged, that is, when refilling is executed.
At least for the two kinds of discharge portions having different discharge amounts of liquid to be discharged, the discharge port of the first discharge portion having the small amount of liquid to be discharged is often structured to be smaller than the discharge port of the second discharge portion having the large amount of liquid to be discharged. The present invention is applicable to the ink jet recording head, which is provided with intermixed discharge portions the discharge ports of which are formed in different sizes, in particular.
Also, the ink jet recording head of the present invention may be structure in such a way that the first discharge portion is provided on the substrate, and provided with a first energy generating element for generating energy to discharge liquid droplet; the first discharge port provided to face the first energy generating element; and a first liquid flow path communicated with the first discharge port for supplying liquid onto the first energy generating element, and the second discharge portion is provided on the substrate, and provided with a second energy generating element for generating energy to discharge liquid droplet; the second discharge port provided to face the second energy generating element; and a second liquid flow path communicated with the second discharge port for supplying liquid onto the second energy generating element, and the opening is provided for the first flow path communicated with the first discharge port.
In this case, the structure may be arranged so that the first discharge portion and the second discharge portion are provided for one substrate, and liquid is supplied from one liquid supply port arranged as a penetrated opening for the substrate to the first liquid flow path and the second liquid flow path, respectively.
Also, for the ink jet recording head of the present invention, the structure may be arranged so that a first liquid supply port for supplying liquid to the first discharge port and a second liquid supply port for supplying liquid to the second discharge port are provided, respectively, and the opening is provided on the projected area of the opening surface of the first liquid supply port.
In accordance with the present invention, if the first discharge port is provided in the plural number, it is preferable to arrange openings corresponding to the first discharge ports each individually. Then, the suction recovery process can be executed for all the discharge portions appropriately.
For the present invention, there are conceivably various modes as to the positions of the opening, the sizes and shapes thereof as those obtaining preferable functions, such as making the liquid flow easier at the time of executing the suction recovery process in the location where mixed bubbles tend to remain, among some others.
In other words, it is preferable for one mode to position the opening more backward in the liquid flow path than the discharge port as observed in the direction of liquid supply to the discharge port. In this case, the size of the opening should preferably be larger than the discharge port on the discharge portion having the large amount of liquid to be discharged.
Also, for another mode, it is preferable for another mode to position the opening more forward in the liquid flow path than the discharge port as observed in the direction of liquid supply to the discharge port. In this case, the size of the opening should preferably be smaller than the discharge port on the discharge portion having the small amount of liquid to be discharged. Also, it is preferable to configure the opening in such a shape that the width of the portion on the side nearer to the discharge port is made larger.
Also, for the structure having the discharge ports communicated with plural discharge portions, which are connected with the supply source of liquid and open in the direction toward the surface where the discharge ports are formed, each opening may be arranged on each supply port or more on the discharge port side than the supply port.
Also, the opening may be arranged on the extend line of the liquid flow path wall that separates the flow path of the discharge portion having the small amount of liquid to be discharged from the liquid flow path of the adjacent discharge portion, which is extended in the direction of liquid supply, or may be arranged on the center line extended from the liquid flow path of the discharge portion having the small amount of liquid to be discharged, which is extended in the direction of liquid supply.
The present invention creates action to perform the suction recovery process in good condition for the ink jet recording head provided with a small discharge portion having a small discharge amount of liquid to be discharged. Therefore, the present invention is preferably applicable to an ink jet recording head that adopts the method in which film boiling is given to liquid by means of electrothermal converting members, which makes highly precise image recording possible by use of small liquid droplets. Particularly, among such methods currently available, this invention is preferably applicable to the ink jet recording head that enables bubbles generated by film boiling to be communicated with the atmosphere.
Also, the ink jet recording apparatus of the present invention is provided with the aforesaid ink jet recording head, and the suction recovery unit, which sucks liquid from the discharge portions of the ink jet recording head.
In accordance with the present invention, the aforesaid suction recovery unit is provided with a cap that covers and airtightly closes the opening surface of the discharge ports, and a suction pump for sucking liquid from the discharge ports and the opening covered by the cap. Here, it may be possible to arrange so that the suction pump sucks liquid from at least the two kinds of discharge portions of the ink jet recording head substantially on the same condition. Further, the cap may cover at least two kinds of discharge port portions together.